Most aromatic polyester polyols used in the production of polyurethane (PU) foams have low functionally in the range of 2-2.5. As the functionality increases to 2.5 so does the viscosity. Typical viscosity of an aromatic polyester polyol with a functionality approaching 2.5 is above 10,000 cps, too high to be used as a sole source of polyol because of the viscosity limitations of PU foam production equipment. Thus, they are combined with high functionally/low viscosity polyether polyols to yield PU foams of commercial value.
Aromatic polyester polyols have been used in polyurethane and polyisocyanurate foams for some time. U.S. Pat. Nos. 4,604,410 and 4,701,477 disclose a method for making rigid polyurethane and polyisocyanurate foams which entails reacting an excess of an organic polyisocyanate with an etherified modified aromatic polyol. The etherified modified aromatic polyol is prepared by digesting recycled polyalkylene terephthalte (PET) polymers with a low molecular weight polyol, such as diethylene glycol. The resulting product is then blended with a low molecular weight polyol, such as alpha methyl glucoside. The intermediate product is etherified with propylene oxide and/or ethylene oxide.
U.S. Pat. No. 4,469,824 teaches a method for making liquid terephthalic esters that are useful as polyol extenders in rigid polyurethane foams and as the sole polyol component in polyisocyanurate foams. The terephthalic esters are made to remain in a liquid form by reacting recycled polyethylene terephthalte (PET) with diethylene glycol and one or more oxyalkylene glycols. Ethylene glycol is then stripped from the reaction to yield a mixture of ester which is free of solids upon standing. Due to solubility limit, a maximum of 5% alpha-methyl glucoside may be added to increase the functionality of the resulting product.
U.S. Pat. No. 4,644,019 discloses a method for preparing isocyanurate foam that is similar to the methods disclosed above but this method includes reacting an ethoxylate of an alkylphenol, preferably nonylphenol with the polyethylene terephthalate while it is being digested.
U.S. Pat. No. 5,360,900 discloses a method to produce a high functionality and a high aromatic content at a conventional viscosity by combining ethoxylated methyl glucoside or propoxylated methyl glucoside with a polyethylene terephthalte base polyester.
None of the above described polyols are capable of being used as the sole polyol in the production of polyurethane foams because they lack sufficiently high functionality. The present invention provides a series of high functional polyester polyols to meet the challenge.